Sagging bending moment causes the beam to bend in a way to make concavity downward (cup-shaped) and it results in developing tensile stress in lower half of the beam x-section.
downward
The rocks called "ballast" provides a cushion that the ties are embedded in. The ballast can shift some as trains pass over while keeping the ties locked in position so that the rails attached by spikes to the ties cannot shift and bend (which can cause the cars to derail).
dangerous bend
Forces bend flex.
Layers of rocks can curve downward due to tectonic forces. When two tectonic plates collide, the pressure and compression can cause the rocks to fold and bend. This folding can create downward curves known as synclines, where the youngest rocks are exposed in the center and older rocks are found on the sides.
Folds are geologic structures that are formed when rocks bend but do not break.
syncline
Syncline.
Flex your foot
Folds are geologic structures that are formed when rocks bend but do not break.
Synclines are downward arches of folded rocks.
...known as syncline
rocks
It is called folding when rocks bend without breaking because of plate movement.
It is called folding when rocks bend without breaking because of plate movement.
Metamorphic rock i think?